There are forestry machines in the form of a feller buncher having a carrier(wheeled or tracked) and a disk saw felling head attached to the front end of the carrier. The felling head has a spinning disk saw at the bottom of the felling head. A plurality of cutting teeth is mounted to the periphery of the spinning disk saw at spaced-apart intervals.
The disk saw is massive and acts as a flywheel which is spun up to operating speed by a hydraulic pump and motor circuit. The disk saw fells trees by kinetic energy, not hydraulic power. Thus, rotational speed of the disk saw is needed and recovery of rotational speed is important to the ability to fell the next tree. The felling operation pulls down the speed of the disk saw after cutting through the tree. The longer the operator must wait for the disk saw to return to operating speed, the less productive the felling operation. Depending upon the extent of speed loss, the disk saw may take several seconds to recover to operating speed.
Such forestry machines typically indicate speed of the disk saw by measuring the pressure change of the hydraulic fluid on a mechanical gauge; that is, high pressure indicates low, increasing speed and low pressure indicates high, steady state operating speed or a “ready to fell” condition. Such gauges are somewhat vulnerable to damage, can leak, and may be difficult to see. A tachometer may also be used, but is likewise hard to see and interpret.